Transparent inorganic-organic hybrid materials via aqueous sol-gel processing

ABSTRACT

A sol to form an inorganic-organic hybrid coating having a thick highly transparent hard coating is described. The hybrid coating is formed from a combined aqueous sol with least one hydrolyzable silane and at least one hydrolyzable metal oxide precursor where the only organic solvents present are those liberated upon hydrolysis of the silanes and metal oxide precursors. In one embodiment an inorganic-organic hybrid coating is formed by combination of a sol, prepared by the hydrolysis of tetraethoxysilane and γ-glycidoxypropyltrimethoxysilane with an excess of water, and a sol, prepared by the hydrolysis of titanium tetrabutoxide and γ-glycidoxypropyltrimethoxysilane with a deficiency of water. A plastic substrate can be coated with the combined sol and the combined sol gelled to a thickness of at least 5 μm with heating to less than 150° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage application of InternationalPatent Application No. PCT/US2009/056618, filed Sep. 11, 2009, whichclaims the benefit of U.S. Provisional Application Ser. No. 61/110,435,filed Oct. 31, 2008, the disclosures of which are hereby incorporated byreference in their entireties, including any figures, tables, ordrawings.

BACKGROUND OF THE INVENTION

Transparent coatings from sol-gel techniques that closely approximateinorganic glasses are commonly formed from alcohols or other non-aqueoussolvents. For example, to obtain a continuous transparent coating, aTiO₂ glass is often formed from condensation of a tetraalkoxytitanate inthe presence of a chelating agent in an alcohol solvent or underrestricted conditions, such as synthesis in a glove box. Aqueoussolvents, or even using a large quantity of water during the process,generally promote the condensation of precursors into particulateglasses. Even when non-aqueous solvents are used, the formation of ahard robust coating is problematic as the resulting glasses often have atendency to crack because of shrinkage induced stresses upon evaporationof solvents and the loss of condensation byproducts. Because of thispropensity for cracking, coating thicknesses in excess of 1.5 μmgenerally require that multiple thin coating layers are made, usuallywith practical limits of 20 to 30 coats. The formation of thick singlelayer coatings is often achieved in a non-aqueous system by the use ofan inorganic/organic composite, an organically modified ceramic, wherean organic component is included in a colloidal sol-gel system.Generally there is little interpenetration of these inorganic andorganic portions, and high hardness with optical transparency isgenerally not achieved in such systems.

As the use of organic polymer based devices, such as LCD displays andLED lighting, increases, there is a greater need for thick superiorabrasive resistant transparent coatings that have excellent barrierproperties for plastic or other organic substrates, and where theprocessing can be carried out with the formation of a single coatinglayer in a manner that does not damage the underlying substrate. Hencethe formation of a transparent hard coating with high solids that act asan excellent diffusion barrier for an underlying substrate remains aneed.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention are directed to an inorganic-organic hybridcoating where a sol-gel glass is derived from a sol having at least onehydrolyzable silane, where at least one silane contains at least onepolymerizable organic group attached to the silane, and at least onehydrolyzable metal oxide precursor. The sol is free of organic solventsin excess of that which can be formed upon hydrolysis of the silane andmetal oxide precursor. The silanes are of the structure R_((4-n))SiX_(n)where: n is 1 to 4; X is independently a hydrolyzable group selectedfrom C₁ to C₆ alkoxy, Cl, Br, I, hydrogen, C₁ to C₆ acyloxy, and NR′R″where R′ and R″ are independently H or C₁ to C₆ alkyl, C(O)R′″, whereR′″ is independently H, or C₁ to C₆ alkyl; and R is independently C₁ toC₁₂ radicals, optionally with one or more heteroatoms, including O, S,NH, and NR″″ where R″″ is C₁ to C₆ alkyl or aryl. The radical can not behydrolyzed from the silane and contains a group capable of undergoingpolyaddition or polycondensation reactions, selected from Cl, Br, I,unsubstituted or monosubstituted amino, amido, carboxyl, mercapto,isocyanato, hydroxyl, alkoxy, alkoxycarbonyl, acyloxy, phosphorous acid,acryloxy, metacryloxy, epoxy, vinyl, alkenyl, or alkynyl. In oneembodiment the silanes are tetraethoxysilane (TEOS) andγ-glycidoxypropyltrimethoxysilane (GPTMS). The metal oxide precursor canbe MX_(n) where: n is 2 to 4; M is a metal selected from the groupconsisting of Ti, Zr, Al, B, Sn, and V; and X is a hydrolyzable moietyselected from the group C₁ to C₆ alkoxy, Cl, Br, I, hydrogen, and C₁ toC₆ acryloxy. In one embodiment, the metal oxide precursor comprisestitanium tetrabutoxide (TTB).

The sol and subsequent coating can contain dispersed nanoparticles thatare oxides, oxide hydrates, nitrides, or carbides of Si, Al, B, Ti, orZr in the shape of spheres, needles, or platelets. For example, thenanoparticles can be SiO₂, TiO₂, ZrO₂, Al₂O₃, Al(O)OH, Si₃N₄ or mixturesthereof. Typical nanoparticles can be 2 to 50 nm in cross section. Inone embodiment, the nanoparticles can be boehmite rods, platelets, or acombination thereof.

Other embodiments of the invention are directed to a method for coatinga substrate with an inorganic-organic hybrid material of a combined solwith the compositions described above, where at least one silicate sol,having at least one hydrolyzable silane, where at least one of thesilanes has at least one polymerizable organic group attached to thesilane and a stoichiometric excess of water, is added to a metal oxidesol, having at least one metal oxide and at least one hydrolyzablesilane having at least one polymerizable organic group attached to thesilane with less than a stoichiometric amount of water relative to thesilanes and metal oxide precursors, to form the combined sol. Thiscombined sol is coated on a substrate and gelled to form a coating thatis transparent to visible light. The coating with a thickness of atleast 2 μm has a transmittance of at least 95%. In embodiments of theinvention, nanoparticles can be dispersed in the combined sol. Coatingcan be carried out by any technique including dipping, spreading,brushing, knife coating, rolling, spraying, spin coating, screenprinting, and curtain coating. Gelling can be carried out at ambientconditions or by heating as constrained by the substrate upon which thecoating is formed. For example the substrate can be an organic materialsuch as a thermoplastic and gelation can be carried out below the glasstransition temperature of the thermoplastic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a photographic reproduction of vials containing combinedsols compositions where a fixed titanate-silicate sol was combined withepoxysilicate-silicate sols with various proportions of epoxysilicate tosilicate precursors as indicated in Table 1 according to an embodimentof the invention.

FIG. 2 shows a photographic reproduction of vials containing combinedsols compositions where a fixed epoxysilicate-silicate sols (B) ratiowas combined with an epoxysilicate-titanate sol (A) with variousproportions of epoxysilicate to titanate precursors, as indicated inTable 2, according to an embodiment of the invention.

FIG. 3 is a plot of compositions of γ-glycidoxypropyltriethoxysilane(GPTMS), titanium tetrabutoxide (TBT), and tetraethoxysilane (TEOS) thatresult in transparent combined sols that do not display gelation withinthree hours of mixing to form a combined sol according to embodiments ofthe invention.

FIG. 4 is a plot of percent transmittance verses wavelength for twofilms from 60 GPTMS:30 TBT:10 TEOS film of about 3.6 μm according to anembodiment of the invention formed by dip coating a glass slide in acombined sol.

FIG. 5 is a plot of nanoindention measurements for an 80 GPTMS:10TBTL:10 TEOS film prepared from an aqueous system according to anembodiment of the invention and an equivalent film prepared from anorganic solvent.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are directed to water based sol-gelprocessing that are free of included organic solvents, although organiccompounds that are often used as solvents can be released uponhydrolysis of the sol precursors in the aqueous solvent.Inorganic-organic hybrid materials are formed where organic groupcontaining precursors are hydrolyzed and condensed with inorganicprecursors in the aqueous environment. The inorganic precursors can bethose that form mixed metal oxides of silicon, titanium, aluminum, orzirconium. Unlike common methods where white precipitates are formedbetween these metal oxide precursors in aqueous rich systems, methodsaccording to embodiments of the invention do not form such precipitatesand permit the formation of thick clear crack free glasses on a singledeposition from an aqueous solution. The resulting glasses displaytransparencies of at least 95% in the visible range and display goodmechanical properties. In some embodiments of the invention, variousmetal oxide particles can be dispersed in the glass precursors and curedinto the final glass.

The organic group containing precursor and the inorganic precursor canbe hydrolyzable silanes. The hydrolyzable silane can be any compound ora mixture of compounds with the formula R_((4-n))SiX_(n) where: n is 1to 4 and where X is independently a hydrolyzable group including C₁ toC₆ alkoxy, Cl, Br, I, hydrogen, C₁ to C₆ acyloxy, NR′R″ where R′ and R″are independently H or C₁ to C₆ alkyl, C(O)R′″, where R′″ isindependently H, or C₁ to C₆ alkyl. Particularly useful X groups forembodiments of the invention are C₁ to C₄ alkoxy groups, as volatilealcohols are formed upon hydrolysis. When n is 4, the silane is aninorganic precursor. When n is less than 4, the silane constitutes theorganic group containing precursor. For the organic group containingprecursor, R is independently C₁ to C₁₂ radicals, optionally with one ormore heteroatoms, including O, S, NH, and NR″″ where R″″ is C₁ to C₆alkyl or aryl, wherein the radical is non-hydrolyzable from the silaneand contains a group capable of undergoing a polyaddition orpoly-condensation reaction, including Cl, Br, I, unsubstituted ormonosubstituted amino, amino, carboxyl, mercapto, isocyanato, hydroxyl,alkoxy, alkoxycarbonyl, acyloxy, phosphorous acid, acryloxy,metacryloxy, epoxy, vinyl, alkenyl, or alkynyl. A particularly useful Rgroup is γ-glycidoxypropy, where for example, the compound of formulaR_((4-n))SiX_(n) is γ-glycidoxypropyltrimethoxysilane (GPTMS) orγ-glycidoxypropyltriethoxysilane.

The inorganic precursor can include an additional hydrolyzable metaloxide precursor as well as a silicon oxide precursor were the additionalmetal oxide precursor is one or more compounds of the formula MX_(n)where: n is 2 to 4; M is a metal selected from the group consisting ofTi, Zr, Al, B, Sn, and V; and X is a hydrolyzable moiety selected fromthe group C₁ to C₆ alkoxy, Cl, Br, I, hydrogen, and C₁ to C₆ acryloxy.Ti, Al, and Zr are preferred metals. Again, particularly useful X groupsfor embodiments of the invention are C₁ to C₄ alkoxy groups, as volatilealcohols are formed upon hydrolysis.

The organic group containing precursor can be employed at a level ofabout 20 to about 99 mole percent of the combined precursors to theultimate unfilled gelled coating. A silicon dioxide inorganic precursorcan be employed up to about 70 mole percent of the combined precursorsin the ultimate unfilled gelled coating. The other metal oxide inorganicprecursor can be employed in up to about 40 mole percent of the combinedprecursors. Additionally, in some embodiments of the invention, metaloxide nanoparticles can be suspended as composite fillers in thecombined aqueous sol. The nanoparticles are selected from the oxides,oxide hydrates, nitrides, and carbides of Si, Al, B, Ti, and Zr. Thenanoparticle can be from 1 to 100 nm in diameter, preferably from 2 to50 nm in diameter and more preferably from 5 to 20 nm in diameter. Thenanoparticles can be included in one or more of the sols as a powder, oras a suspension in an aqueous solvent. Among the nanoparticles for usein the invention are SiO₂, TiO₂, ZrO₂, Al₂O₃, Al(O)OH, and Si₃N₄. Thenanoparticles can be in the shape of spheres, needles, platelets, or anyother shape. Advantageously, the nanoparticles are readily dispersed inwater with relatively little aggregation into larger particles.Particular useful particles include the boehmite form of aluminum oxide.For example, rod shaped particles of boehmite can be dispersed at 10 wt% in water, leaving an average particle size of about 10 nm without theformation of larger aggregate particles, as is common in non-aqueoussolvents. Nanoparticles with larger aspect ratios, such as platelets,can form free flowing aqueous suspensions in water, which can becombined with the aqueous sol in embodiments of the invention.

A catalyst for hydrolysis and subsequent condensation of the precursorscan be included in the coating formulation as needed. The catalyst canbe an acid or a base, but is generally and acid. For example the acidcan be nitric acid. Additional catalyst for the polyaddition orpolycondensation reaction of some or all of the R groups of the silanescan be included in the coating formulation. The catalyst can be aphotoinitiator. Optional components that can be included, separately orin combination, in the sol formulations, to achieve the desiredproperties and curing profiles of the ultimate gelled coatings, arecolorants, leveling agents, UV stabilizers, and photosensitizers.

In embodiments of the invention employing inorganic precursors of twodifferent metals, inorganic precursors of one metal and organic groupcontaining precursors are hydrolyzed and condensed to form one sol andinorganic precursors of another metal and organic group containingprecursors are hydrolyzed and condensed to form another sol, where thefinal sol is a combination of the two sols. Advantageously, theindividual or combined sols can be stored for extended periods withoutgelation. The combined sol can ultimately be cast on a surface andpermitted to cure at low temperatures into the desired gel. The two solsthat are combined can differ in the proportions of precursors and water.The inorganic precursors, which hydrolyze readily and condense at aslower rate, are combined with a greater than stoichiometric amount ofwater to form a water rich sol. The sol containing the products frominorganic precursors that rapidly condense after hydrolysis, such astitanium dioxide precursors, are combined with a stoichiometricdeficiency of water. Furthermore, the organic functional groupcontaining precursor that less readily condenses into a gel because ofthe relative kinetic and/or functionality limitations to gelation isoften combined with the deficiency of water before the inclusion of therapidly hydrolyzing and condensing precursor to promotecross-condensation between the inorganic and organic functional groupcontaining precursors and to achieve a sol with unhydrolyzed groupsattached to the condensed aggregates.

In one embodiment of the invention, titanium tetraalkoxides arehydrolyzed and condensed with γ-glycidoxypropoxytrialkoxysilanes andsilicon tetraalkoxides. For example, GPTMS can be mixed with a less thana stoichiometric amount of water with nitric acid present in catalyticproportions to give a partially hydrolyzed mixture. This partiallyhydrolyzed mixture can be generated by agitation at room temperature forshort periods of time, for example about 1 hour. To this partiallyhydrolyzed mixture, a portion of titanium tetrabutoxide (TBT) can beincluded to form a partially condensed epoxysilicate-titanate sol. Inparallel to the preparation of this epoxysilicate-titanate sol, anepoxysilicate sol can be prepared by mixing GPTMS with a largeproportion of water, much greater than stoichiometric, with nitric acidpresent in catalytic proportions to give a fully hydrolyzed mixture.This hydrolyzed mixture can be agitated with tetraethoxysilane (TEOS) atroom temperature for about 3 hours to produce a transparent aqueousepoxysilicate sol. The epoxysilicate-titanate sol and epoxysilicate solcan be combined with vigorous agitation to form a combinedepoxysilicate-titanate sol, which rapidly becomes transparent.

The sols formed according to embodiments of the invention can be used tocoat a wide variety of substrates. The substrates can be any solidmaterial that can be heated to temperatures of about 100° C. or morewithout decomposition or deformation. In particular, organic materialscan be used. In one embodiment, the substrate is a transparentthermoplastic, for example, polycarbonate (PC), polyethylenterephthalate(PET), polyethylenenaphthalate (PEN), or polymethylmethacrylate (PMMA).The gelation of the coating can be promoted at any temperature up toabout 150° C. or higher when the thermal transitions of the substratepermit. In some embodiments of the invention, gelation can be promotedby a catalyst at a temperature below 100° C., for example, using aphotochemically generated acid. In one embodiment of the invention,reaction of the organic functional group on a silane can occurphotochemically when an appropriate catalyst or initiator is included,while the condensation of the hydrolyzed metal alkoxides occursexclusively thermally. For example, if an olefin substituent is includedon a silane incorporated in the reaction mixture, the vinyl additionreaction may be carried out photochemically with inclusion of anappropriate photoinitiator, such as a radical photoinitiator, while thecondensation of the metal alkoxide groups, such as alkoxysilane andalkoxytitanate groups undergo a thermally induced hydrolysis andcondensation.

METHODS AND MATERIALS Preparation of a 60:30:10 Mole RationGPTMS:TBT:TEOS Combined Sol

An epoxysilicate sol was prepared by mixing 3.0 g of GPTMS in 0.5 g ofwater containing nitric acid in a catalytic quantity (H₂O:GPTMS=2.2).The mixture was stirred at room temperature for one hour. To thispartially hydrolyzed GPTMS sol was added 4.3 g of TBT and the mixturestirred for three hours at room temperature to yield a stableepoxysilicate-titanate sol. In a separate container, 3.0 g of GPTMS and10 g of water containing nitric acid in a catalytic quantity(H₂O:GPTMS=44) were mixed to form a sol to which 0.9 g of TEOS wasadded. The resulting transparent epoxysilicate-silicate sol was stirredfor 3 hours at room temperature. The two sols, epoxysilicate-titanateand epoxysilicate-silicate, were mixed to form an opaque suspension thatupon vigorous stirring was transformed into a transparent combined solin approximately two minutes.

Determination of Composition Parameters for the Preparation of ClearSols

Using a method adapted from that above with the exception of theproportions of GPTMS in the epoxysilicate-titanate sol and the combinedsol, the proportions of the various precursors that can formsufficiently stable epoxysilicate-titanate (A) andepoxysilicate-silicate (B) sols was determined. In one series ofexperiments, tabulated in Table 1 below, the amount of TEOS provided tothe final combined sot from the epoxysilicate-silicate sol (B) was heldconstant and the composition of the epoxysilicate-titanate sol (A) washeld constant. In this manner, the proportion of the epoxysilicatevaried for a fixed proportion of titanate to silicate precursors. Theamount of water from the epoxysilicate-silicate (B) andepoxysilicate-titanate (A) sols was constant. As can be seen in Table 1,as the proportion of GPTMS in the mixture decreases in theepoxysilicate-silicate sol (B) and the combined sol, the combined sol isinsufficiently stable for reliably preparing coatings as prematuregelation can occur when the amount of GPTMS present in theepoxysilicate-silicate sol (B) dropped below ⅓ that of the GPTMS presentin the epoxysilicate-titanate sol (A).

TABLE 1 Stability of combined sols for various compositions where afixed titanate- silicate sol (A) was combined withepoxysilicate-silicate sols (B) with various proportions ofepoxysilicate to silicate precursors. Epoxysilicate-titanate solEpoxysilicate-silicate sol GPTMS/ Combine sol (A) Weight in g (B) Weightin g TBT/TEOS Appearance with GPTMS TBT H₂O GPTMS TEOS H₂O Molar ratiotime 3.0 4.3 0.5 3.0 0.9 10 60/30/10 Transparent - 2 min. 3.0 4.3 0.51.5 0.9 10 53/35/12 Transparent - 10 min. 3.0 4.3 0.5 1.0 0.9 1050/37/13 Transparent - 3 hrs 3.0 4.3 0.5 0.5 0.9 10 47/40/14 Translucentsol 3.0 4.3 0.5 0.0 0.9 10 43/43/15 Gelled after mixing

In another series of experiments, tabulated in Table 2 below, the amountof TBT provided to the final combined sol from theepoxysilicate-titanate sol (A) was held constant and the composition ofthe epoxysilicate-silicate sol (B) was held constant. In this manner,the proportion of the epoxy-silicate varied for a fixed proportion oftitanate and silicate precursor. The amount of water from theepoxysilicate-silicate (B) and epoxysilicate-titanate (A) sols wasconstant. As can be seen in Table 2, as the proportion of GPTMS in themixture decreases in the epoxysilicate-titanate sol (A) and the combinedsol, the combined sol is insufficiently stable for reliably preparingcoatings as premature gelation can occur when the molar ratio of GPTMSto TBT in the epoxysilicate-titanate sol (A) dropped below ⅔ that of theepoxysilicate-silicate sol (B).

TABLE 2 Stability of combined sols where a fixed epoxysilicate-silicatesols (B) ratio was combined with an epoxysilicate-titanate sol (A) withvarious proportions of epoxysilicate to titanate precursors.Epoxysilicate-titanate sol Epoxysilicate-silicate sol GPTMS/ Combine solWeight in g Weight in g TBT/TEOS Appearance with GPTMS TBT H₂O GPTMSTEOS H₂O Molar ratio time 3.0 4.3 0.5 3.0 0.9 10 60/30/10 Transparent -2 min. 2.5 4.3 0.5 3.0 0.9 10 58/31/11 Transparent - 10 min. 2.0 4.3 0.53.0 0.9 10 56/33/11 Partial Gelled then degelled 1.5 4.3 0.5 3.0 0.9 1050/37/13 Gelled after mixing 1.0 4.3 0.5 3.0 0.9 10 47/40/14 Gelledafter mixing 0.5 4.3 0.5 3.0 0.9 10 43/43/15 Gelled after mixing

The compositions indicated in Table 1 produced homogeneous mixtureswhere even gelled mixtures appeared nearly homogeneous, as can be seenin FIG. 1 where photographic reproduction of vials containing thesemixtures is shown. In contrast, the gelled compositions in Table 2displayed phase separation as well as gelation, as can be seen in thephotographic reproduction of FIG. 2.

In another series or experiments, tabulated in Table 3, below, theamount of GPTMS, TBT, TEOS, and water provided to the final combined solwas held constant but the amount of the GPTMS in theepoxysilicate-titanate sol and the epoxysilicate-silicate sol was variedand the sols were combined in relative quantities that give a constantproportion of all precursors in the combined sol. As can be seen inTable 3, having a low proportion of GPTMS in either theepoxysilicate-titanate sol (A) or epoxysilicate-silicate sol (B)resulted in an unstable sol. This study indicated that theepoxysilicate-titanate sol (A) can have a GPTMS to TBT ration of 0.5 to2 and that the GPTMS can be distributed between theepoxysilicate-titanate (A) and epoxysilicate-silicate (B) sols at aratio of 0.5 to 11.

TABLE 3 Stability of combined sols from various compositions ofepoxysilicate-silicate sols (B) and titanate-silicate sols (A) to give aconstant composition combined sol. Epoxysilicate-titanate solEpoxysilicate-silicate sol GPTMS titanate/ Combine sol (A) Weight in g(B) Weight in g GPTMS silicate Appearance with GPTMS TBT H₂O GPTMS TEOSH₂O Molar ratio time 6.0 4.3 0.5 0.0 0.9 10 ∞ Transparent - 2 min. 5.54.3 0.5 0.5 0.9 10 11 Transparent - hrs. 5.0 4.3 0.5 1.0 0.9 10 5Transparent - hrs. 4.0 4.3 0.5 2.0 0.9 10 2 Transparent - 10 min. 3.04.3 0.5 3.0 0.9 10 1 Transparent - 2 min. 2.0 4.3 0.5 4.0 0.9 10 0.5Transparent - 5 min. 1.5 4.3 0.5 4.5 0.9 10 0.33 Translucent sol 1.0 4.30.5 5.0 0.9 10 0.2 Gelled after mixing

FIG. 3 shows a plot of the proportions of the GPTMS, TBT, and TEOS inthe combined sols that result in transparent sols and that do not gelwithin three hours of mixing. However, the manner in which the GPTMS isproportioned between the epoxysilicate-silicate sols andtitanate-silicate sols can preclude the formation of a stable sol eventhough the proportions of GPTMS, TBT and TEOS can be within the rangewhere stable sols can be formed.

Optical properties of the films can be excellent for coatings accordingto embodiments of the invention. FIG. 4 shows a plot of percenttransmittance verses wavelength for the two 3.6 μm films from 60GPTMS:30 TBT:10 TEOS film formed by dip coating a glass slide in thecombined sol. The thickness was measured using a Digimatic indicatorproduced by Mitsutoyo. The transmittance was measured using aPerkin-Elmer Lambda 800 UV\VIS Spectrophotometer against an uncoatedglass slide reference. As can be seen from FIG. 4, the film is virtuallytransparent in the visible range.

Films were prepared on a glass substrate from a combined sol of thecomposition 80 GPTMS:10 TBT:10 TEOS, in a manner similar to thatdescribed above and are compared to films prepared from the sameproportion of sol precursors but prepared in an organic solvent system.Nanoindention measurements were taken with a Hysitron Tribolndenter™. Ascan be seen in FIG. 5, the film prepared from the aqueous systemrequired at least twice the load for indentation to an equivalent depth,demonstrating an improved hardness and toughness. The comparativestiffness and toughness are given in Table 4, below.

TABLE 4 Mechanical properties as measured by nanoindentation for an 80GPTMS:10 TBT:10 TEOS film prepared using an aqueous solution and anorganic solvent solution. Aqueous System Organic Solvent SystemStiffness (μN/nm) 30 9 Modulus (GPa) 7.0 2.2

The inorganic-organic hybrid material can also include particulates.Composites were made where the 80 GPTMS:10 TBT:10 TEOS included 40 to 80percent by weight boehmite particles in the form of platelets. Thesuspension of boehmite in the combined sol was deposited on flat glassor PET surfaces. In all cases, no cracking was observed for compositionsthat lead to the hybrid material with up to 60 weight percent boehmite.When composites had 65 weight percent boehmite, cracking was observed inthe coating on PET, while cracking did not occur until 75 weight percentboehmite was included in the coating formed on glass. The 80 GPTMS:10TBT:10 TEOS is not an optimized composition for the sole to form thematrix glass of the boehmite composite. Other sol compositions ordifferent curing and devolatilization conditions can result in anoptimized matrix glass with higher flexibility to permit even higherloadings of particles, for example 75 or even 80 weight percentparticles in the composite.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

We claim:
 1. A method for coating a substrate with an inorganic-organichybrid material comprising the steps of: providing at least one silicatesol comprising water and at least one hydrolyzable silane, wherein atleast one of said silanes comprise at least one polymerizable organicgroup attached to said silane, wherein said silicate sol is free oforganic solvents in excess of those formed upon hydrolysis of saidsilane, and wherein said water is in excess of stoichiometry for thecomplete hydrolysis of said silanes; adding to said silicate sol atleast one metal oxide sol to form a combined sol, wherein said metaloxide sol comprises water, at least one hydrolyzable metal oxideprecursor, and at least one hydrolyzable silane having at least onepolymerizable organic group attached to said silane, wherein said waterin said metal oxide sol is less than stoichiometric for the completehydrolysis of said silane and metal oxide precursor in said metal oxidesol, and wherein said metal oxide sol is free of organic solvents inexcess of those formed upon hydrolysis of said silane and said metaloxide precursor; coating a substrate with said combined sol; and gellingsaid combined sol upon said substrate, wherein said resulting coating istransparent to visible light with a transmittance of at least 95% at athickness of at least 2 μm.
 2. The method of claim 1, wherein saidpolymerizable organic group comprises glycidoxypropyl.
 3. The method ofclaim 1, wherein said silanes comprise γ-glycidoxypropyltrimethoxysilane(GPTMS) and optionally tetraethoxysilane (TEOS).
 4. The method of claim1, wherein said hydrolyzable metal oxide precursor comprises a metalalkoxide.
 5. The method of claim 1, wherein said hydrolyzable metaloxide precursor comprises titanium tetrabutoxide (TBT).
 6. The method ofclaim 1, further comprising the step of dispersing nanoparticles in saidcombined sol.
 7. The method of claim 6 wherein said nanoparticlescomprise boehmite nanoplatelets.
 8. The method of claim 6, wherein saidstep of dispersing comprises adding a dispersion of said nanoparticle inwater.
 9. The method of claim 1, wherein said step of coating comprisesdipping, spreading, brushing, knife coating, rolling, spraying, spincoating, screen printing and curtain coating.
 10. The method of claim 1,wherein said step of gelling comprises heating said coated substrate.11. The method of claim 10, wherein said heating is to a temperatureless than 180° C.
 12. The method of claim 1, wherein said substratecomprises an organic material.
 13. The method of claim 12, wherein theorganic material comprises a thermoplastic.